OSAC Lexicon
The OSAC Lexicon is a compendium of forensic science terms and definitions. This terminology tool was created to help bring consistency and understanding to the way terms are used by the various forensic science. Use of the OSAC Lexicon does not replace the need to reference the original published source.
The terms and definitions in the OSAC Lexicon come from the published literature, including documentary standards and technical reports. It is continually updated with the latest work from OSAC units, as well as terms from newly published documentary standards and standards elevated to the OSAC Registry.
Gradually terms are evaluated and harmonized by the OSAC to a single term. This process results in an OSAC Preferred Term. An OSAC Preferred Term is a term, along with its definition, that has undergone review and evaluation by the FSSB Terminology Task Group and has been approved by the FSSB. The FSSB recommends that subcommittees use OSAC Preferred Terms when drafting standards.
The OSAC Lexicon should be the primary resource for terminology and used when drafting and editing forensic science standards and other OSAC work products.
A type of location search in which a scent match is not indicated by the canine thereby excluding an individual as the scent contributor.
the result of a comparison between two hair samples in which the characteristics of the questioned hair differ from those present in the known hair sample, and therefore the donor of the known sample cannot be included as a possible source of the questioned hair.
Discussion—This result is reached in a comparative hair examination when differences are noted in the macroscopic or microscopic characteristics between the questioned and known hairs; however, the differences are insufficient for an absolute exclusion of a person as a possible source. This could be due to the natural variation that occurs in hairs as a biological specimen, the effect that time or environment can have upon a hair, or the reference sample does not capture the complete variation of the individual's hair.
A conclusion that eliminates an individual as a contributor of DNA obtained from an evidentiary sample based on the comparison of DNA data.
the result of a comparison between two hair samples in which exclusionary differences are observed in the characteristics of the questioned hair that are not present in the known hair sample, and therefore the donor of the known sample can be excluded as a possible source of the questioned hair.
Discussion—This result is reached in a comparative hair examination when exclusionary differences (for example, color, characteristics indicative of ancestry) are noted in the macroscopic or microscopic characteristics between the questioned and known hairs. In these circumstances, the source of the known hairs, as represented by the known sample, is eliminated as a possible source of the questioned hair.
a difference in one or more characteristics between compared items that is sufficient to determine that the compared items did not originate from the same source, are not the same source, or do not share the same composition or classification.
Also referenced in ANSI/ASTM E2228-23a Standard Guide for Microscopical Examination of Textile Fibers, ANSI/ASTM E2227-23e1 Standard Guide for Forensic Examination of Dyes in Textile Fibers by Thin-Layer Chromatography, ANSI/ASTM E2225-23 Standard Guide for Forensic Examination of Fabrics and Cordage, ANSI/ASTM E3295-23 Standard Guide for Using Micro X-Ray Fluorescence (μ-XRF) in Forensic Polymer Examinations, ANSI/ASTM E3316-22 Standard Guide for Forensic Examination of Hair by Microscopy, ANSI/ASTM E3296-22 Standard Guide for Using Pyrolysis Gas Chromatography and Pyrolysis Gas Chromatography-Mass Spectrometry in Forensic Polymer Examinations, ANSI/ASTM E3260-21 Standard Guide for Forensic Examination and Comparison of Pressure Sensitive Tape, ANSI/ASTM E1732-24e1 Standard Terminology Relating to Forensic Science.
Evidence that may be favorable to the accused, impeach the prosecution’s evidence, or mitigate the offense.
The friction ridge prints of an individual, associated with a known or claimed identity,and deliberately recorded electronically, by ink, or by another medium (also called 'known prints').
a specimen of physical evidence of known origin.
The deliberately recorded images or impressions from the friction ridge skin of an individual. NOTE Examples may include, but are not limited to, inked tenprints, inked palm prints, Livescan prints, powder and lift prints, casted/moulded prints, or photographs of friction ridge skin.
The deliberately recorded images or impressions from the friction ridge skin of an individual.
NOTE Examples may include, but are not limited to, inked tenprints, inked palm prints, Livescan prints, powder and lift prints, casted/moulded prints, or photographs of friction ridge skin.
The deliberately recorded images or impressions from the friction ridge skin of an individual. NOTE Examples may include, but are not limited to, inked tenprints, inked palm prints, Livescan prints, powder and lift prints, casted/moulded prints, or photographs of friction ridge skin.
The deliberate recorded images or impressions from the friction ridge skin of an individual.
Circumstances that would cause a reasonable person to believe that relevant prompt action was necessary to prevent physical harm to persons or animals, the destruction of relevant evidence or some other consequence improperly frustrating legitimate law enforcement efforts.
Quantity defining an interval about a result of a measurement that may be expected to encompass a large fraction of the distribution of values that could reasonably be attributed to the measurand. DISCUSSION(1) The fraction may be regarded as the coverage probability or level of confidence of the interval. (2) To associate a specific level of confidence with the interval defined by the expanded uncertainty requires explicit or implicit assumptions regarding the probability distribution characterized by the measurement result and its combined standard uncertainty. The level of confidence that may be attributed to this interval can be known only to the extent to which such assumptions can be justified. (3) An expanded uncertainty U is calculated from a combined standard uncertainty uc and coverage factor k using: U =k X uc.
quantity defining an interval about a result of a measurement that may be expected to encompass a large fraction of the distribution of values that could reasonably be attributed to the measurand.
Discussion—(1) The fraction may be regarded as the coverage probability or level of confidence of the interval.
(2) To associate a specific level of confidence with the interval defined by the expanded uncertainty requires explicit or implicit assumptions regarding the probability distribution characterized by the measurement result and its combined standard uncertainty. The level of confidence that may be attributed to this interval can be known only to the extent to which such assumptions can be justified.
(3) An expanded uncertainty, U, is calculated from a combined standard uncertainty, uc, and coverage factor, k, using: U=k×uc.
The number of distinct alignments expected by chance; the default sorting metric in BLAST search results.
Anyone testing any idea has a strong expectation that leads to an influence about the outcome.
A person displaying special skill and knowledge in a given area derived from training, education, or experience.
The testimony made by a qualified person about a scientific, technical, or professional issue. An expert is often called upon to testify due to his/her familiarity with the subject or special training in the field.
A coherent, scientifically sound statement or statements regarding the meaning of analytical findings in a forensic case that is formulated from a consideration of the synthesis of analytical data, pre-analytical factors, case history, and other relevant information
A material with a pressure ratio (maximum pressure/pressure at ignition, in absolute units) equal to or greater than 2.0 in any test when tested using the explosibility or Go/No-Go screening test described in Section 13 of ASTM E1226, Standard Test Method for Explosibility of Dust Clouds. [68, 2018]
The sudden conversion of potential energy (chemical or mechanical) into kinetic energy with the production and release of gases under pressure, or the release of gas under pressure. These high-pressure gases then do mechanical work such as moving, changing, or shattering nearby materials.
the sudden conversion of potential energy (chemical or mechanical) into kinetic energy with the production and release of gases under pressure, or the release of gas under pressure; these high-pressure gases then do mechanical work such as moving, changing, or shattering nearby materials.
Study of how chemistry, physics, fire science, engineering disciplines of fluid and solid mechanics, and heat transfer interact to influence explosion behavior.
Study of how chemistry, physics, fire science, engineering disciplines of fluid and solid mechanics, and heat transfer interact to influence explosion behavior.
Any chemical compound, mixture, or device that functions by explosion.
a single substance, or a mixture of substances, that is capable of producing an explosion upon initiation (see high explosives and low explosives).
a single chemical compound that can produce an explosion.
Any material that can act as fuel for an explosion.
a mixture of separate fuel and oxidizer components that together can produce an explosion.
the detection, identification, on-site evaluation, rendering safe, recovery, and final disposal of unexploded explosive ordnance; it may also include explosive ordnance which has become hazardous by damage or deterioration.
Discussion—1) This term is also sometimes colloquially applied to the same actions applied to improvised explosive devices (IEDs). (2) The term “render safe” involves procedures utilized by EOD technicians or bomb technicians to make an explosive device safe.
A chemical substance that can be utilized in the production of explosives by either mixing or blending with other substances, or by chemical processing. The vast majority of chemicals are used for legitimate purposes. However, some chemicals could potentially be misused for the illicit manufacture of homemade or improvised explosive. Indeed, relatively small amounts of select chemicals can be applied in certain processes that produce a significant amount of explosives.
material remaining from an explosive deflagration or detonation or from direct contact with an explosive. Explosive residue generally does not have a discernible morphology, can be visible or non-visible, and can contain uninitiated and post-combustion components.
Discussion—Visible explosive residue can be present in large (grams) and small (single particle or single crystal) quantities.
an arrangement of explosive components by which the initial force from the primer is transmitted and intensified until it reaches and detonates the main explosive composition.
A canine trained to detect and alert to the presence of explosives and explosives related substances (e.g., propellants, oxidizers, precursors) for which it has been trained that may be located in the environment.
A canine trained to detect and alert to the presence of explosives and explosives related substances (e.g., propellants, oxidizers, precursors) for which it has been trained that may be located in the environment and/or person borne.
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The side of a structural assembly or object that is directly exposed to the fire.
The parameter, associated with the assessment method used, that characterizes the dispersion of the values that could reasonably be attributed to the measurand.
Physical assessment of the decedent by a medicolegal death investigator.
Diagnostic medical procedure conducted by a pathologist or other specially trained medical personnel that consists of physical inspection of the decedent without internal examination; can include ancillary tests.
An evaluation of practitioner performance against pre-established criteria by means of interlaboratory comparisons. [ISO/IEC 17043:2010]
the condition in which a birefringent particle appears dark when viewed between crossed polarizers.
Discussion—Most fibers exhibit extinction when their long axis is oriented parallel to the privileged direction of one of the polarizing filters.
A procedure where the reinforcement of a previously reinforced behavior is discontinued with the intention to reduce the occurrence of that behavior
To cause to cease burning.
Total cellular DNA isolated from a biological sample to include nuclear and mitochondrial DNA.
any plot of signal intensity observed at a chosen m/z value or set of values in a series of mass spectra recorded as a function of time.